In a typical PTCA procedure, a guiding catheter having a preformed distal tip is percutaneously introduced into a patient's peripheral artery, e.g. femoral or brachial artery, by means of a conventional Seldinger technique and advanced therein until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guide wire is first advanced by itself through the guiding catheter until the distal tip of the guide wire extends beyond the arterial location where the procedure is to be performed. Then a catheter is mounted onto the proximal portion of the guide wire which extends out of the proximal end of the guiding catheter which is outside of the patient. The catheter is advanced over the guide wire, while the position of the guide wire is fixed, until the operative element on the catheter is disposed within the arterial location where the procedure is to be performed. After the procedure is performed, the catheter may be withdrawn from the patient over the guide wire or the guide wire may be repositioned within the coronary anatomy for an additional procedure.
Conventional guide wires for angioplasty, stent delivery, atherectomy and other intravascular procedures usually have an elongate core member with one or more segments near the distal end thereof which taper distally to smaller cross sections. A flexible body member, such as a helical coil or a tubular body of polymeric material, is typically disposed about and secured to at least part of the distal portion of the core member. A shaping member, which may be the distal extremity of the core member or a separate shaping ribbon which is secured to the distal extremity of the core member, extends through the flexible body and is secured to the distal end of the flexible body by soldering, brazing or welding; or an adhesive may be used in the case of a polymeric flexible body which forms a rounded distal tip. The leading tip is highly flexible in order not to damage or perforate the vessel. The portion behind the distal tip becomes increasingly stiff, the better to support a balloon catheter or similar device.
A major requirement for guide wires is that they have sufficient column strength to be pushed through a patient's vascular system or other body lumen without buckling. However, they must also be flexible enough to avoid damaging the blood vessel or other body lumen through which they are advanced. Efforts have been made to improve both the strength and flexibility of guide wires to make them more suitable for their intended uses, but these two properties are for the most part diametrically opposed to one another in that an increase in one usually involves a decrease in the other.
In order to fulfill these requirements, guide wires now typically include two different types of material joined together with a connecting tube, or sleeve, so that a proximal core will consist of a material having sufficient column strength and a distal core will be made of a flexible material to lead the advance through a body lumen. Currently, a nitinol hypotube or connecting tube is used as a sleeve to join a proximal stainless steel core to a nitinol distal core on certain types of guide wires. An example of this type of guide wire can be seen in, for example, U.S. Pat. Nos. 6,248,082 and 6,602,208 (Jafari). The reason that an external tube is used to achieve the connection is because direct welding of nitinol to stainless steel has proven to be difficult if not effectively impossible. Attempts to achieve such a weld are met with serious deficiencies in the resulting strength and unique behavioral properties of nitinol. Furthermore, cracking may occur at the interface between the two metal portions at the weld. However, when this problem is overcome by connection with an external connecting tube, the presence of the tube disadvantageously adds to the profile of the guide wire, tending to obstruct elements of the catheter that must slide along the guide wire during operation.
One prior solution to the general problem of connecting stainless steel to nitinol has been to insert an intermediate vanadium alloy transition piece between the stainless steel piece and the nitinol piece, welding the outer two metal pieces to the inner transition piece. However, in the context of microwelding very small metal pieces, such as portions of a guide wire that may measure between about 0.040 and 0.010 inches diameter at the section to be joined, even this solution may cause deficiencies in the strength and behavioral properties of nitinol due to the high temperature required to melt vanadium. It will be appreciated that welding small work pieces together provides less opportunity for heat to escape from the site of the weld, thus permitting heat buildup at the location of the weld to the detriment of the metal properties and the eventual uniformity and quality of the weld.
Thus, a need exists for an improved guide wire, and method for manufacture, that will address the needs of the prior art. It is believed that the present invention addresses these and other needs.